Systems and methods for automatic sensor registration and configuration

ABSTRACT

Various approaches to ensuring safe operation of industrial machinery in a workcell include disposing multiple image sensors proximate to the workcell and acquiring, with at least some of the image sensors, the first set of images of the workcell; registering the sensors to each other based at least in part on the first set of images and, based at least in part on the registration, converting the first set of images to a common reference frame of the sensors; determining a transformation matrix for transforming the common reference frame of the sensors to a global frame of the workcell; registering the sensors to the industrial machinery; acquiring the second set of images during operation of the industrial machinery; and monitoring the industrial machinery during operation thereof based at least in part on the acquired second plurality of images, transformation, and registration of the sensors to the industrial machinery.

RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalPatent Application No. 62/724,945, filed Aug. 30, 2018, the entiredisclosure of which is hereby incorporated by reference.

TECHNICAL FIELD

The present invention relates, in general, to sensors in athree-dimensional (3D) space, and, in particular, to systems and methodsfor performing automatic estimation of a sensor's position andorientation in 3D space.

BACKGROUND

Industrial machinery is often dangerous to humans. Some machinery isdangerous unless it is completely shut down, while other machinery mayhave a variety of operating states, some of which are hazardous and someof which are not. In some cases, the degree of hazard may depend on thelocation or distance of the human with respect to the machinery. As aresult, various types of “guarding” equipment have been developed toseparate humans and machines, thereby preventing machinery from causingharm to humans. One very simple and common type of guarding is a cagethat surrounds the machinery, configured such that opening the door ofthe cage causes an electrical circuit to place the machinery in a safestate (e.g., shutting down the machinery). This ensures that humans cannever approach the machinery while it is operating in an unsafe state.

More sophisticated types of guarding may involve, for example, opticalsensors. Examples include light curtains that determine if any objecthas intruded into a region monitored by one or more light emitters anddetectors, and two-dimensional (2D) LIDAR sensors that use activeoptical sensing to detect the minimum distance to an obstacle along aseries of rays emanating from the sensors (and thus can be configured todetect either proximity or intrusion into pre-configured 2D zones). Inaddition, 3D depth sensors have been recently employed in variousmachine-guarding applications for providing guarding improvement.Examples of the 3D depth sensors include 3D time-of-flight cameras, 3DLIDAR, and stereo vision cameras. These sensors offer the ability todetect and locate intrusions into the area surrounding industrialmachinery in 3D, which gives them several advantages over 2D sensors.For example, a 2D LIDAR system guarding the floorspace around anindustrial robot will have to stop the robot when an intrusion isdetected well over an arm's-length distance away from the robot, becauseif the intrusion represents a person's legs, that person's arms could bemuch closer and would be undetectable by the 2D LIDAR. However, a 3Dsystem can allow the robot to continue to operate until the personactually stretches his or her arm towards the robot. This allows for amuch tighter coupling between the actions of the machine and the actionsof the human, which provides flexibility in many applications and savesspace on the factory floor, which is always at a premium.

Because human safety is at stake, guarding equipment (particularly theelectronic versions) must comply with stringent industry standardsregarding functional safety, such as IEC 61508 and ISO 13849. Thesestandards specify failure rates for hardware components and rigorousdevelopment practices for both hardware and software components; asystem is considered safe for use in an industrial setting only when thehardware and software components comply with the standards.Standards-compliant systems must ensure that dangerous conditions andsystem failures can be detected with very high probability, and that thesystem responds to such events by transitioning the equipment beingcontrolled into a safe state. For example, safety systems may be tunedto favor false positives over false negatives in order to avoidhazardous consequences resulting from the false negatives.

Separation of humans and machines, however, is not always optimal forproductivity. For example, some tasks are best performed by a human andmachine working collaboratively; machines typically provide morestrength, faster speed, more precision, and more repeatability, whilehumans may offer flexibility, dexterity, and judgment far beyond theabilities of even the most advanced machines. An example of a potentialcollaborative application is the installation of a dashboard in acar—the dashboard is heavy and difficult for a human to maneuver buteasy for a machine, and attaching it requires a variety of connectorsand fasteners that require human dexterity and flexibility to handlecorrectly. Conventional guarding technology, however, is insufficientlyflexible and adaptable to allow this type of collaboration. Therefore,these situations are typically resolved either by automating aspects ofthe task best performed by a human, often at great expense andcomplication, or using a human worker to perform aspects of the taskbetter done by a robot (perhaps using additional equipment such aslift-assist devices) and tolerating potentially slow, error-prone, andinefficient execution that may lead to repetitive stress injuries orexposure to hazardous situations for human workers.

Although improved guarding based on 3D sensing may enable industrialengineers to design processes where each subset of the task is optimallyassigned to a human or a machine without sacrificing the safety of humanworkers, several challenges inherently exist in using the 3D sensors ina safety-critical environment. First, the sensor itself must meetfunctional safety standards. In addition, the raw output of a 3D sensorcannot be used directly in most applications since it is much richer andharder to analyze than the data provided by 2D sensors. 3D sensor datathus requires processing in novel ways to generate effective andreliable control outputs for industrial machinery. Another challengewith systems based on 3D data is the difficulty in configuring andregistering the systems and 3D sensors. In fact, even with 2D sensors,configuring safety guarding can be challenging. First, specific zonesare usually designed and configured for each use case, taking intoaccount the specific hazards posed by the machinery, the possibleactions of humans in the workspace, the workspace layout, and thelocation and field of view of each individual sensor. It can bedifficult to calculate the optimal shapes of exclusion zones, especiallywhen trying to preserve safety while maximizing available floor spaceand system throughput.

Thus, configuring guarding technology requires advanced skill sets ortools. Mistakes in the configuration can result in serious safetyhazards, requiring significant overhead in design and testing. All ofthis work must be completely redone if any changes are made to theworkspace. The extra degree of freedom presented by 3D systems/sensorsresults in a much larger set of possible configurations and hazards,thereby requiring higher levels of data processing in order to generateuseful, reliable control outputs from raw 3D sensor data. Accordingly,there is a need for approaches that reliably monitor a workspace forproviding human safety to operate around the machinery, while reducingthe required processing time and complexity of the data acquired by the3D sensors.

SUMMARY

Various embodiments of the present invention provide systems and methodsfor monitoring a workspace for safety purposes using 3D sensors that areregistered with respect to each other and with respect to one or morepieces of machinery under control. As used herein, the term “register”refers to the process of estimating the relative pose of an object(e.g., a sensor) with respect to one or more other objects (e.g., arobot, the floor, other sensors, etc.). The goal of “registration” is tospecify this relationship in terms of a rigid-body transformation withrespect to a reference frame.

Registration among the sensors may be established based on one or more3D images of the workspace acquired by the sensors when there issufficient overlap and/or distinction between the acquired images. Forexample, conventional computer-vision techniques (e.g., globalregistration algorithms) and a fine registration approach (e.g., an ICPalgorithm) may be implemented to perform registration among the sensors.If there is insufficient overlap between the fields of the sensorsand/or insufficient details in the workspace are provided in theacquired images, one or more registration objects having distinctivesignatures in 3D may be utilized for sensor registration. Alternatively,each sensor may record images of one or more people, moving equipment orother registration object(s) standing in the workspace or passingthroughout the workspace over a period of time; when a sufficient numberof at least partially matching images are acquired, the images may becombined and processed to establish the sensor registration. After thesensor registration is complete, a common reference frame of the sensorsmay then be transformed to a global reference frame of the workspacesuch that the data acquired by the sensor can be processed in the globalframe.

In various embodiments, after the sensors are registered amongthemselves, the sensors are registered to machinery in the workspace.The registration can be established using the machinery and/or aregistration target having a distinctive 3D signature and a related posewith respect to the machinery. For example, the sensors may firstregister to the registration target; and then based on this registrationand the related pose of the registration target to the machinery, thesensors may register to the machinery. In some embodiments, an image ofthe scene in the workspace viewed by the sensors is provided on a userinterface. In addition, a 2D or 3D model of the machinery and/or theworkspace created using computer-aided design (CAD) and/or scanning ofthe actual machinery and/or workspace may be displayed on the image ofthe scene. One or more pairs of discrete features and/or constraints inthe image of scene may then be selected manually by the operator orautomatically by a control system to establish the registration betweenthe sensors and the machinery. In various embodiments, automatedregistration of the sensors to the machinery involves use of aregistration library including one or more configuration parameters(e.g., a number of iterations for fine-tuning the registration, a 3Dpoint cloud density, mesh density, one or more convergence criteria,etc.) that are established in previous setups of the sensors andmachinery in the workspace. In one embodiment, the state of the robot(s)and/or machinery in the image of the scene is compared against that ofthe robot(s) and/or machinery in the stored images of the scene in theregistration library; an image that provides the best matching state inthe registration library can be identified. Subsequently, theconfiguration parameter(s) associated with the best-matched state in theimage of the scene can be retrieved, and based thereon, registration ofthe sensors to the machinery may be established.

During operation of the machinery, registration among sensors andbetween the sensors and machinery can be continuously monitored in realtime. For example, a set of metrics (e.g., registration validation,real-time robot tracking, etc.) capturing the fit accuracy of theobserved data to a model of static elements in the workspace may becreated during the registration process. Upon completion of theregistration and as the system operates, the metrics may be continuouslymonitored and updated in real time. If the metrics or deviations thereoffrom their initial values (i.e., obtained during initial registration)exceed a specified threshold, the registration during the systemoperation may be considered to be invalid and an error condition may betriggered. Subsequently, the machinery under operation may be shut downor transitioned to a safe state. In addition, the signals acquired bythe sensors during operation of the machinery may be continuouslyanalyzed. If the sensors remain in position but the fields of view areobscured or blocked, and/or the measured sensor signals are degraded,the machinery may be transitioned to a safe state as well. Accordingly,various embodiments provide approaches that reliably monitor theworkspace for providing human safety to operate around the machinery.

Accordingly, in one aspect, the invention relates to a method ofensuring safe operation of industrial machinery in a workcell. Invarious embodiments, the method comprises the steps of disposing aplurality of image sensors proximate to the workcell and acquiring, withat least some of the image sensors, a first plurality of images of theworkcell; registering the sensors to each other based at least in parton the first plurality of images and, based at least in part on theregistration, converting the first plurality of images to a commonreference frame of the sensors; determining a transformation matrix fortransforming the common reference frame of the sensors to a global frameof the workcell; registering the plurality of sensors to the industrialmachinery; acquiring a second plurality of images during operation ofthe industrial machinery; and monitoring the industrial machinery duringoperation thereof based at least in part on the acquired secondplurality of images, transformation, and registration of the sensors tothe industrial machinery. In one embodiment, the method further includesimplementing a global-optimization algorithm to register (i) themultiple sensors to each other and (ii) the multiple sensors to theindustrial machinery.

The first plurality of images may be computationally analyzed to verifythat there is sufficient overlap and sufficient distinction thereamong.In some embodiments, wherein the industrial machinery comprises at leasta robot arm. The method may, in certain embodiments, further compriseproviding at least one entity having a distinctive 3D signature in theworkcell, the first plurality of images comprising images of the atleast one entity.

In various embodiments, the method further comprises separatelyregistering each of the sensors to the entity, and registering thesensors to each other based at least in part on the separateregistration of each sensor to the entity. In some cases at least one ofthe sensors is visible to the entity, in which case the method mayfurther comprise the steps of registering the at least one sensor to theentity, and registering the plurality of sensors to the industrialmachinery based at least in part on the registration of the visiblesensor to the entity, the registration of the sensors to each other anda related pose of the entity with respect to the industrial machinery.In addition, the method may further include receiving an external input(e.g., a user input or an input transmitted from a controllercontrolling the entity) for identifying a state (e.g., an orientation, aposition, etc.) of the entity.

The method may further comprise the steps of providing an image of ascene in the workcell; determining one or more pairs of discretefeatures on the image of the scene; and registering the plurality ofsensors to the industrial machinery based at least in part on the one ormore pairs of discrete features. In various embodiments, the image ofthe scene comprises at least one of the first plurality of images; 3Dpoint cloud data mapping the workcell; and/or a 2D or 3D CAD model of atleast one of the industrial machinery or the workcell.

In some embodiments, the method further comprises performing a 2D or 3Dscan on the industrial machinery or the workcell, where the image of thescene comprises a model of the industrial machinery or the workcellconstructed based at least in part on the 2D or 3D scan. In some cases,prior to the registering step, a registration library comprising aplurality of images of the industrial machinery is established, witheach image associated with at least one configuration parameter. A stateof the industrial machinery in the image of the scene may becomputationally compared against states of the industrial machinery inthe plurality of images in the registration library, and the image inthe registration library providing the best matching state of theindustrial machinery to the state of the industrial machinery in theimage of the scene is identified. The plurality of sensors may then beregistered to the industrial machinery based at least in part on theconfiguration parameter corresponding to the identified image in theregistration library. The configuration parameter may, for example,comprise a number of iterations for fine-tuning the registration of thesensors to the industrial machinery, a number of 3D point cloud data permesh, and/or a convergence criterion.

In various embodiments, the method further comprises the steps ofanalyzing the first plurality of images to determine an area in theworkcell covered by fields of view of the sensors and, based on theanalysis, identifying at least one of the determined area, areas notcovered by the fields of the view of the sensors, a pose for at leastone of the sensors for achieving an optimal scene coverage, or aplacement location for an additional sensor. Based on the identifiedpose, the pose of the corresponding sensors may be adjusted.

The method may further comprise the step of projecting into the workcella signal or one or more light beams that outline the area covered by thefields of view of the sensors. Alternatively or in addition, the methodmay comprise the step of projecting onto an augmented reality or virtualreality device an image of the workcell and the outline of the areacovered by the fields of view of the sensors.

The method may, in various embodiments, further comprise generating aninitial accuracy metric indicating an accuracy level of the registrationof the plurality of sensors to the industrial machinery, and then,during operation of the industrial machinery, determining whether asubsequent accuracy metric indicating an accuracy level of theregistration deviates from the initial accuracy metric by more than athreshold amount, and if so, altering operation of the industrialmachinery. The latter step may comprise periodically analyzing thesecond plurality of images acquired during operation of the industrialmachinery to (i) regenerate the accuracy metric, (ii) compare theregenerated accuracy metric to the initial accuracy metric to determinea deviation therebetween, and (iii) alter operation of the machinery ifthe deviation exceeds a threshold value. The metric may comprise atleast one of registration validation or real-time robot tracking.

In another aspect, the invention pertains to a control system forensuring safe operation of industrial machinery in a workcell. Invarious embodiments, the system comprises a plurality of image sensorsproximate to the workcell; and a controller configured to acquire, withat least some of the image sensors, a first plurality of images of theworkcell; register the sensors to each other based at least in part onthe first plurality of images and, based at least in part on theregistration, convert the first plurality of images to a commonreference frame of the sensors; determine a transformation matrix fortransforming the common reference frame of the sensors to a global frameof the workcell; register the plurality of sensors to the industrialmachinery; acquire a second plurality of images during operation of theindustrial machinery; and monitor the industrial machinery duringoperation thereof based at least in part on the acquired secondplurality of images, transformation, and registration of the sensors tothe industrial machinery. In one embodiment, the controller is furtherconfigured to implement a global-optimization algorithm to register (i)the multiple sensors to each other and (ii) the multiple sensors to theindustrial machinery.

The controller may be further configured to computationally analyze thefirst plurality of images to verify that there is sufficient overlap andsufficient distinction thereamong. In some embodiments, the industrialmachinery includes at least a robot arm. In addition, the control systemmay further include one or more entities having a distinctive 3Dsignature in the workcell; the first plurality of images includes imagesof the entity/entities.

In various embodiments the controller is further configured toseparately register each of the sensors to the entity; and register thesensors to each other based at least in part on the separateregistration of each sensor to the entity. In some cases one or moresensors are visible to the entity, in which case the controller may befurther configured to register the sensor(s) to the entity; and registerthe multiple sensors to the industrial machinery based at least in parton the registration of the visible sensor(s) to the entity, theregistration of the sensors to each other and a related pose of theentity with respect to the industrial machinery. In addition, the systemmay further include the second controller for controlling the entity andan input module for receiving an external input (e.g., a user input oran input transmitted from the second controller) for identifying a state(e.g., an orientation, a position, etc.) of the entity.

The controller may be further configured to provide an image of a scenein the workcell; determine one or more pairs of discrete features on theimage of the scene; and register the multiple sensors to the industrialmachinery based at least in part on the one or more pairs of discretefeatures. In various embodiments, the image of the scene includes atleast one of the first plurality of images; 3D point cloud data mappingthe workcell; and/or a 2D or 3D CAD model of the industrial machineryand/or the workcell.

In some embodiments, the controller is further configured to cause a 2Dor 3D scan on the industrial machinery or the workcell; the image of thescene includes a model of the industrial machinery or the workcellconstructed based at least in part on the 2D or 3D scan. In some cases,the controller is further configured to, prior to the registering step,establish a registration library including multiple images of theindustrial machinery, each associated one or more configurationparameters; computationally compare a state of the industrial machineryin the image of the scene against states of the industrial machinery inthe multiple images in the registration library; identify one of themultiple images in the registration library providing a best matchingstate of the industrial machinery to the state of the industrialmachinery in the image of the scene; and register the multiple sensorsto the industrial machinery based at least in part on the configurationparameter(s) corresponding to the identified image in the registrationlibrary. The configuration parameter(s) may, for example, include anumber of iterations for fine-tuning the registration of the sensors tothe industrial machinery, a number of 3D point cloud data per mesh,and/or a convergence criterion.

In various embodiments, the controller is further configured to analyzethe first plurality of images to determine an area in the workcellcovered by fields of view of the sensors; and based on the analysis,identify the determined area, areas not covered by the fields of theview of the sensors, a pose for at least one of the sensors forachieving an optimal scene coverage, and/or a placement location for anadditional sensor. In addition, the controller may be further configuredto cause the pose of the corresponding sensors to be adjusted based onthe identified pose.

The controller may be further configured to project, into the workcell,a signal or one or more light beams that outline the area covered by thefields of view of the sensors. Alternatively or additionally, thecontroller may be further configured to project, onto an augmentedreality or virtual reality device, an image of the workcell and theoutline of the area covered by the fields of view of the sensors.

The controller, in various embodiments, is further configured togenerate an initial accuracy metric indicating an accuracy level of theregistration of the multiple sensors to the industrial machinery; andthen, during operation of the industrial machinery, determine whether asubsequent accuracy metric indicating an accuracy level of theregistration deviates from the initial accuracy metric by more than athreshold amount, and if so, alter operation of the industrialmachinery. In the later step, the controller may be further configuredto periodically analyze the second plurality of images acquired duringoperation of the industrial machinery to (i) regenerate the accuracymetric, (ii) compare the regenerated accuracy metric to the initialaccuracy metric to determine a deviation therebetween, and (iii) alteroperation of the machinery if the deviation exceeds a threshold value.The metric may include registration validation and/or real-time robottracking.

As used herein, the term “substantially” means ±10%, and in someembodiments, ±5%. Reference throughout this specification to “oneexample,” “an example,” “one embodiment,” or “an embodiment” means thata particular feature, structure, or characteristic described inconnection with the example is included in at least one example of thepresent technology. Thus, the occurrences of the phrases “in oneexample,” “in an example,” “one embodiment,” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same example. Furthermore, the particular features,structures, routines, steps, or characteristics may be combined in anysuitable manner in one or more examples of the technology. The headingsprovided herein are for convenience only and are not intended to limitor interpret the scope or meaning of the claimed technology.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, with an emphasis instead generally being placedupon illustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIG. 1 is a perspective view of a monitored workspace in accordance withvarious embodiments of the present invention;

FIG. 2 schematically illustrates a control system in accordance withvarious embodiments of the present invention;

FIG. 3 is a flow chart illustrating an approach for registering sensorsamong themselves in accordance with various embodiments of the presentinvention;

FIGS. 4A-4C are flow charts illustrating exemplary approaches forregistering one or more sensors to machinery in a workspace inaccordance with various embodiments of the present invention;

FIGS. 5A and 5B are flow charts illustrating exemplary approaches forconfiguring sensors to appropriately cover a scene in a workspace inaccordance with various embodiments of the present invention; and

FIG. 6 is a flow chart illustrating an approach for validatingregistrations among sensors and between the sensors and machinery duringoperation of machinery in accordance with various embodiments of thepresent invention.

DETAILED DESCRIPTION A. Workspace

Refer first to FIG. 1, which illustrates a representative 3D workspace100 monitored by a sensor system 101 including one or more sensorsrepresentatively indicated at 102 ₁, 102 ₂, 102 ₃. The sensors 102 ₁₋₃may be conventional optical sensors such as cameras, e.g., 3Dtime-of-flight cameras, stereo vision cameras, or 3D LIDAR sensors orradar-based sensors, ideally with high frame rates (e.g., between 30 Hzand 100 Hz). The mode of operation of the sensors 102 ₁₋₃ is notcritical so long as a 3D representation of the workspace 100 isobtainable from images or other data obtained by the sensors 102 ₁₋₃. Asshown in the figure, sensors 102 ₁₋₃ may collectively cover and canmonitor the workspace 100, which includes a robot 106 controlled by aconventional robot controller 108. The robot 106 interacts with variousworkpieces W, and a human operator H in the workspace 100 may interactwith the workpieces W and the robot 106 to perform a task. The workspace100 may also contain various items of auxiliary equipment 110. As usedherein the robot 106 and auxiliary equipment 110 are denoted asmachinery in the workspace 100.

In various embodiments, data obtained by each of the sensors 102 ₁₋₃ istransmitted to a control system 112. In addition, the sensors 102 ₁₋₃may be supported by various software and/or hardware components 114 ₁₋₃for changing the configurations (e.g., orientations and/or positions) ofthe sensors 102 ₁₋₃; as further described below, the control system 112may be configured to adjust the sensors so as to provide optimalcoverage of the monitored area in the workspace 100. The volume of spacecovered by each sensor—typically a solid truncated pyramid or solidfrustum—may be represented in any suitable fashion, e.g., the space maybe divided into a 3D grid of small (5 cm, for example) cubes or “voxels”or other suitable form of volumetric representation. For example, a 3Drepresentation of the workspace 100 may be generated using 2D or 3D raytracing, where the intersections of the 2D or 3D rays emanating from thesensors 102 ₁₋₃ are used as the volume coordinates of the workspace 100.This ray tracing can be performed dynamically or via the use ofprecomputed volumes, where objects in the workspace 100 are previouslyidentified and captured by the control system 112. For convenience ofpresentation, the ensuing discussion assumes a voxel representation, andthe control system 112 maintains an internal representation of theworkspace 100 at the voxel level.

FIG. 2 illustrates, in greater detail, a representative embodiment ofthe control system 112, which may be implemented on a general purposecomputer. The control system 112 includes a central processing unit(CPU) 205, system memory 210, and one or more non-volatile mass storagedevices (such as one or more hard disks and/or optical storage units)212. The control system 112 further includes a bidirectional system bus215 over which the CPU 205, functional modules in the memory 210, andstorage device 212 communicate with each other as well as with internalor external input/output (I/O) devices, such as a display 220 andperipherals 222 (which may include traditional input devices such as akeyboard or a mouse). The control system 112 also includes a wirelesstransceiver 225 and one or more I/O ports 227. The transceiver 225 andI/O ports 227 may provide a network interface. The term “network” isherein used broadly to connote wired or wireless networks of computersor telecommunications devices (such as wired or wireless telephones,tablets, etc.). For example, a computer network may be a local areanetwork (LAN) or a wide area network (WAN). When used in a LANnetworking environment, computers may be connected to the LAN through anetwork interface or adapter; for example, a supervisor may establishcommunication with the control system 112 using a tablet that wirelesslyjoins the network. When used in a WAN networking environment, computerstypically include a modem or other communication mechanism. Modems maybe internal or external, and may be connected to the system bus via theuser-input interface, or other appropriate mechanism. Networkedcomputers may be connected over the Internet, an Intranet, Extranet,Ethernet, or any other system that provides communications. Somesuitable communications protocols include TCP/IP, UDP, or OSI, forexample. For wireless communications, communications protocols mayinclude IEEE 802.11x (“Wi-Fi”), Bluetooth, ZigBee, IrDa, near-fieldcommunication (NFC), or other suitable protocol. Furthermore, componentsof the system may communicate through a combination of wired or wirelesspaths, and communication may involve both computer andtelecommunications networks.

The CPU 205 is typically a microprocessor, but in various embodimentsmay be a microcontroller, peripheral integrated circuit element, a CSIC(customer-specific integrated circuit), an ASIC (application-specificintegrated circuit), a logic circuit, a digital signal processor, aprogrammable logic device such as an FPGA (field-programmable gatearray), PLD (programmable logic device), PLA (programmable logic array),RFID processor, graphics processing unit (GPU), smart chip, or any otherdevice or arrangement of devices that is capable of implementing thesteps of the processes of the invention.

The system memory 210 may contain a series of frame buffers 235, i.e.,partitions that store, in digital form (e.g., as pixels or voxels, or asdepth maps), images obtained by the sensors 102 ₁₋₃; the data mayactually arrive via I/O ports 227 and/or transceiver 225 as discussedabove. The system memory 210 contains instructions, conceptuallyillustrated as a group of modules, that control the operation of CPU 205and its interaction with the other hardware components. An operatingsystem 240 (e.g., Windows or Linux) directs the execution of low-level,basic system functions such as memory allocation, file management andoperation of the mass storage device 212. At a higher level, and asdescribed in greater detail below, an imaging module 242 may registerthe images acquired by the sensors in the frame buffers 235; an analysismodule 237 may analyze the images acquired by the sensors 102 ₁₋₃ todetermine, for example, whether there is sufficient overlap and/ordistinction between the acquired images and/or the coverage areamonitored by the sensors 102 ₁₋₃; a registration module 239 may registerthe sensors among themselves based on the images registered in the framebuffers 235 and/or register the sensors 102 ₁₋₃ to the machinery in theworkspace as further described below; and an input module 241 forreceiving one or more external input data from, for example, the display220, the peripherals 222, the robot controller 108 and/or additionalsensors (e.g., other than the sensors 102 ₁₋₃) for identifying a state(e.g., an orientation, a position, etc.) of the robot 106 and/or one ormore registration objects as further described below. The determinedcoverage area may be stored in a space map 245, which contains avolumetric representation of the workspace 100 with each voxel (or otherunit of representation) labeled, within the space map, as describedherein. Alternatively, the space map 245 may simply be a 3D array ofvoxels, with voxel labels being stored in a separate database (in memory210 or in mass storage 212).

In addition, the control system 112 may communicate with the robotcontroller 108 to control the operation or machinery in the workspace100 using conventional control routines collectively indicated at 250.As explained below, the configuration of the workspace may well changeover time as persons and/or machines move about; the control routines250 may be responsive to these changes in operating machinery to achievehigh levels of safety. All of the modules in system memory 210 may becoded in any suitable programming language, including, withoutlimitation, high-level languages such as C, C++, C#, Java, Python, Ruby,Scala, and Lua, utilizing, without limitation, any suitable frameworksand libraries such as TensorFlow, Keras, PyTorch, or Theano.Additionally, the software can be implemented in an assembly languageand/or machine language directed to the microprocessor resident on atarget device

B. Sensor Registration and Monitoring

The sensor system 101 is implemented to monitor the workspace 100, andthe guarding mechanism is generally configured with respect to dangerousmachinery (e.g., the robot 106), as opposed to the sensors 102 ₁₋₃. In amulti-sensor system, a registration among the sensors 102 ₁₋₃ thatcorrelates the precise location of each sensor 102 with respect to allother sensors is typically established during setup and/or duringoperation of the machinery. In one embodiment, the sensor registrationis performed manually. For example, the human operator H may measuredistances between the focal points of the sensors and the machinerybeing controlled in three dimensions and manually manipulate the poses(e.g., positions and/or orientations) of the sensors 102 ₁₋₃ basedthereon so as to provide an optimal coverage area in the workspace 100.Additionally or alternatively, a user interface shown in the display 220may, for example, provide alignment points of the sensors 102 ₁₋₃ and asignal to indicate optimal sensor positioning to maximize signal qualityand reliability, determine and display metrics for registrationreliability and safety signals, and provide user feedback. The operatorH may then adjust the pose of the sensor 102 ₁₋₃ based on the userfeedback. While it is possible for sensor registration to be achievedmanually, it may be burdensome even for a single sensor, and unrealisticfor providing sufficiently accurate measurements to combine informationfrom multiple sensors. Therefore, in various embodiments, the sensorregistration is performed automatically using suitable computer-visiontechniques. As further described below, approaches for registeringmultiple sensors 102 ₁₋₃ in the workspace 100 are sufficiently simple soas to allow for ease of setup and reconfiguration.

1) Registration Among Sensors

Assuming for simplicity that each frame buffer 235 stores an image(which may be refreshed periodically) from a particular sensor 102, theregistration module 239 may perform registration among the sensors 102₁₋₃ by comparing all or part of the image from each sensor to the imagesfrom other sensors in the frame buffers 235, and using conventionalcomputer-vision techniques (e.g., global-registration algorithms) toidentify correspondences in those images. Suitable global-registrationalgorithms, which do not require an initial registration approximation,generally fall into two categories: feature-based methods andintensity-based methods. Feature-based methods, such as random sampleconsensus (RANSAC), may extract features (e.g., edges) in the images andthen identify correspondences based on the extracted image features;intensity-based methods may determine image intensities in the imagesand then use correlation metrics to compare the intensity patterns. Oncean approximate or gross registration is performed, a fine registrationapproach (e.g., an iterative closest point (ICP) algorithm or suitablevariant thereof) may be performed to fine-tune the registration andcomplete the sensor registration among themselves. Thereafter, the dataacquired by the sensors 102 ₁₋₃ can be processed in a common referenceframe (e.g., in the same coordinate system) based on the registration.

In various embodiments, the common reference frame of the sensors 102₁₋₃ is transformed to a “global” frame (e.g., a coordinate system) ofthe workspace 100. For example, to convert the images acquired by thesensors 102 ₁₋₃ in a common 2D frame to 3D data in the global frame ofthe workspace 100, a 2D range image in the frame buffer 235 may betransformed to a sensor-local 3D coordinate system by undistorting theimage coordinates of each range pixel and applying an inverse projectiontransformation to the undistorted image coordinates and a rangemeasurement. This generates a structured point cloud in the sensor-localcoordinate system, which may be transformed using a suitable rigid-bodytransformation. Referring again to FIG. 1, in one embodiment, thetransformation is determined using one or more “registration objects”120 having distinctive visual signatures in 3D. For example, theregistration object(s) may be placed in a location within the workspacewhere it can be seen by all sensors or at least one sensor that isregistered with respect to the others. By acquiring images of theregistration object(s) using the registered sensor(s) 102 ₁₋₃ and basedon the known signature(s) and/or geometries of the registrationobject(s), the transformation that transforms data in the common frameof the sensors 102 ₁₋₃ to the data in the global frame of the workspace100 may be computed. Thereafter, the data acquired by the sensors 102₁₋₃ can be processed in the global frame of the workspace 100.

The above-described approaches for sensor registration are suitable whenthere is sufficient overlap between the fields of view of the sensors102 ₁₋₃ and sufficient visual detail in the workspace 100 to providedistinct sensor images. If, however, there is insufficient overlapbetween the fields of the sensors 102 ₁₋₃ and/or insufficient detail inthe workspace 100, use of one or more registration objects 120 havingdistinctive signatures in 3D may be necessary to facilitate sensorregistration. For example, each sensor 102 may be first separatelyregistered to the registration object(s); registration among the sensors102 ₁₋₃ may then be established based on the registration between eachsensor 102 and the registration object(s) 120. As used herein, the term“distinctive 3D signature” refers to a uniquely identifiable positionand pose (and so free of rotational or translational symmetry), e.g.,presenting a detectably different profile when viewed from differentangles. For example, while a single cube has six potential orientations,two cubes at a known distance and non-collinear orientation with respectto each other may provide sufficient information for a distinctive 3Dsignature. More generally, the registration object(s) may include, forexample, fiducials or other 2D or 3D objects, and may be stationary orcarried around by the human operator H and/or machinery (e.g., on therobot) in the guarded workspace 100.

Alternatively, registration among the sensors 102 ₁₋₃ may be achieved byhaving each of the sensors 102 ₁₋₃ record images of one or more people,moving equipment (such as automated guided vehicles) or otherregistration object(s) 120 standing in the workspace or passing throughthe workspace over a period of time; when a sufficient number of atleast partially matching images are acquired, the images may be combinedand processed to establish an accurate sensor registration using theapproaches described above.

Occasionally, the data collected from the sensors 102 ₁₋₃ may be noisyor optically distorted; thus, in some embodiments, suitable techniques,such as sub-frame combination, noise reduction, meshing and resampling,etc. may be implemented to minimize (or at least reduce) the noiseinherent in the sensor signals, thereby improving accuracy of sensorregistration. In addition, the detected sensor signals may be correctedusing conventional approaches based on average or distributionestimation so as to maintain sensor alignment. In one embodiment, thenoise and distortion correction process bounds the errors inherent inthe detected signals and registration process. The error bounds can beused as inputs to the control system 112 during operation of the robot106 to ensure human safety. For example, if the noise or distortion ofthe signals detected by the sensors 102 ₁₋₃ during operation of therobot 106 exceeds the error bounds and/or the robotic system driftsoutside the error bounds during operation, the control system 112 mayautomatically communicate with the robot controller 108 so as to switchthe machinery in the workspace 100 to a safe state (e.g., having areduced speed or being deactivated).

In various embodiments, a global-optimization algorithm is implementedto estimate the optimal configuration or pose of each sensor in thecoordinate system of the workspace 100 by minimizing a global errormetric. The use of a global optimization algorithm ensures the bestsensor configuration estimate regardless of the initial configuration orestimates thereof. For example, given a set of correspondences, onecommon approach is to minimize the sum of pairwise (typically Euclidean)distances. In such cases the cost for optimization purposes is taken asthe distance. Other distance-based costs such as “Hausdorff” distanceare common for alignment tasks. Where no correspondences can beidentified, these may be estimated through refinement of a good guessusing nearest neighbor or projections into depth images. Global poseestimation without correspondences is more challenging and the costfunction becomes more abstract, e.g., a search for viable poses viabranch-and-bound algorithms or sampling of point sets to find minimalfunctioning correspondence sets using, e.g., the RANSAC algorithm orsimilar approaches.

FIG. 3 is a flow chart illustrating an exemplary approach 300 forregistering sensors among themselves. In a first step 302, each of thesensors 102 ₁₋₃ may acquire one or more images of the workspace; theimages may be stored in the frame buffer 235 in memory 210. In a secondstep 304, suitable techniques may be optionally implemented to minimize(or at least reduce) the noise and/or correct distortions in thedetected sensor signals. In a third step 306, the analysis module 237may analyze the images to determine whether there is sufficient overlapand/or distinction between the acquired images. If so, the registrationmodule 239 may implement conventional computer-vision techniques (e.g.,global registration algorithms) and a fine registration approach (e.g.,an ICP algorithm) to establish registration among the sensors 102 ₁₋₃(step 308). If there is insufficient overlap between the fields of thesensors 102 ₁₋₃ and/or insufficient details in the workspace 100, one ormore registration objects 120 having distinctive signatures in 3D may beidentified (step 310). Each sensor 102 may be first separatelyregistered to the registration object(s) (step 312). Subsequently, theregistration among the sensors 102 ₁₋₃ may then be established based onthe registration between each sensor 102 and the registration object(s)120 (step 310). Alternatively, each sensor may record images of one ormore people, moving equipment or other registration object(s) 120standing in the workspace or passing throughout the workspace over aperiod of time (step 314). When a sufficient number of at leastpartially matching images are acquired, the images may be combined andprocessed to establish an accurate sensor registration (step 316).Optionally, after registration, the common reference frame of thesensors 102 ₁₋₃ may be transformed to a global frame of the workspace100 (step 318).

2) Registration of Sensors to Machinery

Registration of the sensors 102 ₁₋₃ to the machinery under control inthe workspace 100 can, in some cases, be achieved without any additionalinstrumentation, especially when the machinery has a distinctive 3Dsignature (e.g., a robot arm) and/or when the machinery is visible to atleast one sensor 102 that is registered with respect to the othersensors as described above. The sensor(s) 102 to which the machinery isvisible may first register to the machinery; based on this registrationand the registration among the sensors 102 ₁₋₃, other sensors to whichthe machinery is invisible may then register to the machinery.Alternatively, a registration target (e.g., the registration object 120having a distinctive 3D signature) in the workspace 100 may be utilizedto register the sensors 102 ₁₋₃ to the machinery. Generally, theregistration target is specially designed such that it isstraightforward for the human operator H to determine the pose of theregistration target with respect to the machinery. Again, the sensors102 ₁₋₃ may then be registered to the machinery via registration of thesensors 102 ₁₋₃ to the registration target and the pose of theregistration target relative to the machinery.

In various embodiments, the user interface shown on the display 220 mayprovide an image of the scene in the workspace 100 to allow the humanoperator H to manually designate certain parts of the image as keyelements of the machinery under control. The registration of the sensors102 ₁₋₃ to the machinery may then be performed using the user-designatedkey elements. The image of the scene may include the actual scene viewedby the sensors 102 ₁₋₃ or one or more additional sensors (e.g., RGBcameras) employed in the workspace 100. In addition, the image of thescene may include visible 3D point cloud data mapping the workspace 100.In one embodiment, the image of the scene includes geometry of at leasta portion of the registration target. For example, the geometry mayinclude a 2D or 3D CAD model of the machinery (e.g., the robot) and/orthe workspace 100. Additionally or alternatively, the geometry mayinclude a model of the actual machinery and/or workspace constructedbased on a 2D and/or 3D scan captured by the sensors 102 ₁₋₃ (and/orother similar sensors), machinery or other equipment in the workspace100. In cases where the robot 106 and/or other machinery controlled bythe robot controller 108 is used as the registration target, theposition of the robot and/or other machinery in the workspace 100received and determined by the robot controller 108 may be combined withthe CAD model thereof to obtain the fully posed geometry correspondingto the state of the workspace 100. In addition, the robot controller 108and/or the control system 112 may continuously monitor the position ofthe robot and/or other machinery to ensure that no undesirable movementoccurs while the scan data are acquired and accumulated.

The CAD model may be imprecise; thus, in some embodiments, varioussuitable techniques can be implemented to improve fit and quality of theCAD model. For example, floors and walls outside of a workcell(enclosing, for example, the machinery under control and the humanoperator H) in the workspace 100 may be excluded from the image of thescene and/or the CAD model to improve the registration accuracy. In oneembodiment, the CAD model is simplified by taking out or deletingextraneous model components that do not contribute to registration;alternatively, the CAD model may be simplified into its minimumcomponents, such as a stick figure. In some embodiments, the dataacquired by the sensors 102 ₁₋₃ can be used to improve the accuracy ofthe 2D or 3D CAD model by incorporating, for example, robot dresspackages and/or end effectors as part of the model. In one embodiment,the 2D or 3D CAD model can also be overlaid on top of the point clouddata or visual image acquired by the sensors 102 ₁₋₃ on the userinterface shown on the display 220 as an alignment aid.

It should be noted that the geometry of the machinery used forregistration is not necessarily the same one used for collisionavoidance. Typically, collision geometry includes cabling and a dresspackage associated with the machinery and is biased towards inclusionfor safety. On the other hand, registration geometry is unbiased, withdifferent resolution and precision requirements, excludes non-rigidregions, and may have to exclude regions that provide unreliablemeasurements (e.g., dark or overly reflective surfaces or componentsthat are thin and hard to measure). As described above, in someembodiments, the registration geometry of the registration target and/orworkcell is constructed by scanning the actual registration targetand/or workcell using the same or similar sensors as the ones that areused to perform registration (as opposed to the CAD model). This maylead to more reliable reference geometry that is not subject todeviations between the CAD model and the actual manufactured parts ofthe robot, whether intended or accidental.

The alignment/registration of the sensor system 101 to the machinery canbe performed manually through the user interface. For example, the usermay use a keyboard input, a mouse, a joystick or other suitable tools tospecify the pose of each sensor, a group of sensors with known poseswith respect to each other and/or with respect to the machinery shown onthe display 220. This process can be automated or semi-automated. Yetanother option to perform the alignment/registration is to select pairsof discrete features in the depth image and on the robot 106 shown onthe user interface on the display 220, followed by an automated orsemi-automated refinement step. For example, the human operator H or theregistration module 239 may introduce a constraint by picking a singlepair of features, and then trigger automatic registration of the sensorsystem 101 to the machinery in the presence of the constraint (i.e.,ensuring the constraint to be satisfied); the constraint may improvereliability of the registration. In some embodiments, two constraintsare added manually by the operator H or automatically by theregistration module 239; this may further restrict the search space andmake the automatic registration even more robust. Selecting three pairsof features may allow skipping a search for coarse featurecorrespondences, and instead going directly to the refinement step (suchas using the ICP algorithm discussed above), thereby providing areliable and accurate registration.

Referring again to FIG. 2, in various embodiments, automatedregistration of the sensors 102 ₁₋₃ to the machinery involves use of aregistration library 255; the registration library 255 includes one ormore configuration parameters (such as a number of iterations forfine-tuning the registration, a number of 3D point cloud data per mesh,one or more convergence criteria, etc.) that are established in previoussetups of the sensor system 101 and machinery in the workspace 100.Typically, each configuration parameter in the registration library 255is established for a particular spatial arrangement of one or morespecific robots 106, machinery, hardware configuration, and/or sensors102 ₁₋₃ in the workspace 100, and is stored along and in associationwith the respective image of the scene in the memory 210. In oneembodiment, the control system 112 (e.g., the registration module 239)automatically compares the state (e.g., the orientation, position, etc.)of the robot(s) and/or machinery in the image of the scene against thatof the robot(s) and/or machinery in the stored images of the scene inthe registration library 255 and then identifies a stored image thatprovides the best matching state. The control system 112 (e.g., theregistration module 239) may then retrieve the configurationparameter(s) associated with the best-matched state in the image of thescene, and based thereon, perform automated registration of the sensors102 ₁₋₃ to the machinery.

Occasionally, a single state of the robot or other machinery in theworkspace 100 may not provide a registration target that adequatelyconstrains all degrees of freedom (because, for example, not all sensors102 ₁₋₃ can observe the robot 106 in its current configuration and/orthe robot features observed by the sensors 102 ₁₋₃ are not sufficientlydistinctive as described above); in various embodiments, the robot 106and/or other machinery can be re-posed to one or more additional knownstates (e.g., the states that have been successfully set up previouslyfor registration), either manually or automatically by the robotcontroller 108 and the control system 112 running a predeterminedprogram. Data related to the state(s) of the robot 106 and/or othermachinery and the data acquired by the sensors 102 ₁₋₃ during thisprocedure can be combined to provide a larger registration data set thatprovides a more reliable and precise registration. In one embodiment,the combined data may be compared against the data stored in theregistration library 255 so as to allow automated registration of thesensors 102 ₁₋₃ to the machinery as described above. In addition, thedata acquired during re-posing of the robot 106 and/or other machineryto the additional known state(s) may be stored in the registrationlibrary 255 for further comparison.

FIGS. 4A-4C are flow charts illustrating exemplary approaches forregistering one or more sensors to machinery in a workspace. Referringfirst to FIG. 4A, in a first step 402, the machinery under control inthe workspace is analyzed by, e.g., the control system 112, to determinewhether it has a distinctive 3D signature and/or is visible to at leastone sensor that is registered with respect to the other sensors. Forexample, if the images acquired by the sensors 102 ₁₋₃ indicate that themachinery does not have rotational or translational symmetry in at leastone dimension (e.g., a different profile of the machinery is presentedwhen being viewed from a different angle), the machinery is determinedto have a distinctive 3D signature. If so, the registration module 239may first register to the machinery the sensor(s) 102 to which themachinery is visible (step 404). Based on the registration performed instep 404 and the registration among the sensors 102 ₁₋₃, theregistration module 239 may then register to the machinery other sensorsto which the machinery is invisible (step 406). If the machinery doesnot have a distinctive 3D signature and/or is invisible to any sensorsthat are registered with respect to the other sensors, the registrationmodule 239 may identify a registration target having distinctivesignatures in 3D in the workspace (based on, for example, the imagesacquired by the sensor(s)) and determine the pose of the registrationtarget with respect to the machinery (step 408). Subsequently, theregistration module 239 may register the sensors 102 ₁₋₃ to theregistration target (step 410), and based on the registration in step410 and the related pose of the registration target to the machinery,register the sensors 102 ₁₋₃ to the registration target (step 512).

Alternatively, referring to FIG. 4B, in various embodiments, an image ofthe scene in the workspace 100 viewed by the sensors 102 ₁₋₃ and/oradditional sensor(s) is provided on a user interface shown on thedisplay 220 (step 422). Optionally, the analysis module 237 may analyzethe sensor images and provide visible 3D point cloud data mapping theworkspace 100 on the image of the scene (step 424). In addition, thecontrol system 212 may create a 2D or 3D CAD model of the machineryand/or the workspace 100 and display the model on the image of the scene(step 426). Additionally or alternatively, the sensors 102 ₁₋₃ (and/orother similar sensors), machinery or other equipment in the workspace100 may perform a 2D and/or 3D scan on the actual machinery and/orworkspace and construct a model thereof based on the scan (step 428). Inone implementation, the position of the robot and/or other machinery inthe workspace 100 received and determined by the robot controller 108may be combined with the model created in step 426 or 428 to obtain thefully posed geometry thereof corresponding to the state of the workspace100 (step 430). In various embodiments, one or more pairs of discretefeatures in the depth image and on the robot 106 shown on the userinterface are selected manually by the operator or automatically by thecontrol system 112 (step 432). Based thereon, the registration module239 may perform registration using, for example, refinement stepsdescribed above (step 434). Additionally or alternatively, theregistration module 239 may introduce one or more constraints by pickingone or more pair of features on the image of the scene (step 436), andthen performing automatic registration of the sensor system 101 to themachinery in the presence of the constraint(s) (step 438).

Referring to FIG. 4C, in various embodiments, automated registration ofthe sensors 102 ₁₋₃ to the machinery involves use of a registrationlibrary 255. In a step 442, a registration library 255 including one ormore configuration parameters (such as a number of iterations forfine-tuning the registration, a number of 3D point cloud data per mesh,one or more convergence criteria, etc.) is created. In a second step444, the registration module 239 automatically compares the state of therobot(s) and/or machinery in the image of the scene against that of therobot(s) and/or machinery in the stored images of the scene in theregistration library 255 and then identifies a stored image thatprovides the best matching state. The registration module 239 may thenretrieve the configuration parameter(s) associated with the best-matchedstate in the image of the scene (step 446), and based thereon, performautomated registration of the sensors 102 ₁₋₃ to the machinery (step448). Optionally, the control system 112 and the robot controller 108may re-pose the robot 106 and/or other machinery to one or moreadditional known states (e.g., states that have been successfullyemployed previously for registration) (step 450). Data related to thestate(s) of the robot 106 and/or other machinery and the data acquiredby the sensors 102 ₁₋₃ during this procedure can be combined to providea larger registration data set (step 452). In one embodiment, thecombined data can then be compared against the data stored in theregistration library 255 to identify the image having the best matchingstate as described in step 446 (step 454). Subsequently, theregistration module 239 can retrieve the configuration parameter(s)associated with the best-matched state in the image of the scene (step446), and based thereon, perform automated registration of the sensors102 ₁₋₃ to the machinery (step 448). In some embodiments, the dataacquired during re-posing of the robot 106 and/or other machinery to theadditional known state(s) is stored in the registration library 255(step 456).

3) Configuration of Sensors to Appropriately Cover a Scene

To determine an appropriate setup of the 3D sensors 102 ₁₋₃ for bestproviding coverage of an area in the workspace 100, variousconsiderations, such as occlusions caused by objects relative to thesensors 102 ₁₋₃, must be considered. In various embodiments, the userinterface shown on the display 220 provides an interactive 3D displaythat shows the coverage of all sensors 102 ₁₋₃ to aid in configuration.If the system is configured with sufficient high-level information aboutthe machinery being controlled, such as the location(s) of a dangerouspart or parts of the machinery and the stopping time and/or distance,the control system 112 (e.g., the analysis module 237) may be configuredto provide intelligent feedback as to whether the configuration of thesensors 102 ₁₋₃ provides sufficient coverage, and/or suggest placementfor additional sensors.

In some embodiments, the feedback further includes, for example, asimple enumeration of the areas that are not covered by the fields ofthe view of the sensors 102 ₁₋₃ and/or proposed sensor locations forachieving the optimal scene coverage. In order to achieve optimalplacement of the sensors 102 ₁₋₃, in various embodiments, the analysismodule 237 may, based on the feedback, cause a light source (not shown)to project onto the workspace 100 a signal or one or more light beamsthat outline the monitored coverage of the sensors 102 ₁₋₃ and/or theproposed location for each sensor. The human operator H may then placeor adjust the sensors 102 ₁₋₃ based on the proposed sensor locationsand/or the outlined coverage. In addition, the control system 112 (e.g.,the analysis module 237) may aid the operator H in sensor placementthrough an augmented reality or virtual reality device that projects animage of the workspace 100 and the sensor coverage onto the display 220(or a headset). The operator H may place/adjust the sensors based ontheir locations shown on the image on the display 220. Theplacement/adjustment of the sensors 102 ₁₋₃ may be automated. Forexample, as described above, the sensors 102 ₁₋₃ may be supported bysoftware/hardware components 114 ₁₋₃ that are configured to change theposes and positions of the sensors 102 ₁₋₃. In various embodiments,based on the feedback provided by the analysis module 237, the controlsystem 112 may be configured to adjust the software/hardware components114 ₁₋₃ so as to achieve the optimal scene coverage of the sensors 102₁₋₃. In one implementation, the control system 112 further operates themachinery (e.g., move the robot via the controller 108) to a locationthat can be observed by all (or at least most) sensors 102 ₁₋₃, therebyimproving the accuracy of the registration, as well as dynamicallydetermining occlusions or unsafe spaces that cannot be observed by thesensors 102 ₁₋₃; these are marked as unsafe areas in the workspace 100.

In various embodiments, the control system 112 can be programmed todetermine the minimum distance from the machinery at which it mustdetect a person in order to stop the machinery by the time the personreaches it (or a safety zone around it), given protective separationdistances determined by the industrial standards, the robot or machinemanufacturer, or through a dynamic model of the machinery (whichincludes conservative estimates of walking speed and other factors).Alternatively, the required detection distance can be input directlyinto the control system 112 via the display 220. The control system 112can then analyze the fields of view of all sensors 102 ₁₋₃ to determinewhether the workspace 100 is sufficiently covered to detect allapproaches. If the sensor coverage is insufficient, the control system112 may propose new locations for existing sensors 102 ₁₋₃, and/orlocations for additional sensors, that may remedy the coveragedeficiency. Otherwise, the control system 112 may default to a safestate and not permit any machinery to operate unless the analysis module237 verifies that all approaches can be monitored effectively by thesensors 102 ₁₋₃.

In some instances, there are areas that the sensors 102 ₁₋₃ cannotobserve sufficiently to ensure safety, but that are guarded by othermeans such as cages, etc. In this case, the user interface can beconfigured to allow the human operator H to indicate to the controlsystem 112 that these areas may be considered safe, overriding thesensor-based safety analysis and/or any built-in inherent safetyanalysis.

FIGS. 5A and 5B are flow charts illustrating exemplary approaches forconfiguring sensors to appropriately cover a scene in a workspace.Referring first to FIG. 5A, in a first step 502, the user interfaceshown on the display 220 may provide an interactive 3D display thatshows the coverage of all sensors 102 ₁₋₃. If the system is configuredwith sufficient high-level information about the machinery beingcontrolled, the control system 112 will provide intelligent feedbackregarding the coverage area provided by the configuration of the sensors102 ₁₋₃, e.g., as a simple enumeration of the areas that are not coveredby the fields of the view of the sensors 102 ₁₋₃, proposed sensorlocations for achieving an optimal scene coverage, and/or suggestedplacement for additional sensors (step 504). In one embodiment, theanalysis module 237 may, based on the feedback, cause a light source toproject onto the workspace 100 a signal or one or more light beams thatoutline the monitored coverage of the sensors 102 ₁₋₃ and/or theproposed location for each sensor (step 506). Additionally oralternatively, the analysis module 237 may cause an augmented reality orvirtual reality device to project an image of the workspace 100 and thesensor coverage onto the display 220 (step 508). Based on the feedbackprovided by the analysis module 237 and/or the projected sensor coverageand/or the proposed locations of the sensors, the control system 112 maybe configured to adjust the software/hardware components 114 ₁₋₃associated with the sensors so as to adjust the poses thereof, therebyachieving the optimal scene coverage (step 510). Optionally, the controlsystem 112 further operate the machinery (e.g., moving the robot) to alocation that can be observed by all (or at least most) sensors 102 ₁₋₃(step 512), thereby improving the accuracy of the registration, as wellas dynamically determining occlusions or unsafe spaces that cannot beobserved by the sensors 102 ₁₋₃ (step 514).

Alternatively, referring to FIG. 5B, the control system 112 can beprogrammed to determine the minimum distance from the machinery at whichit must detect a person in order to stop the machinery by the time theperson reaches it (step 522). In some embodiments, the requireddetection distance can be input directly into the control system 112(step 524). The control system 112 can then analyze the fields of viewof all sensors 102 ₁₋₃ to determine whether the workspace 100 issufficiently covered to detect all approaches (step 526). If the sensorcoverage is insufficient, the control system 112 may propose newlocations for existing sensors 102 ₁₋₃, and/or locations for additionalsensors that may remedy the coverage deficiency (step 528). Otherwise,the control system 112 may default to a safe state and not permit anymachinery to operate unless the analysis module 237 verifies that allapproaches can be monitored effectively by the sensors 102 ₁₋₃ (step530).

4) Registration Validation During System Operation

Once the registrations among the sensors 102 ₁₋₃ and between the sensors102 ₁₋₃ and the machinery have been achieved, it is critical that thesensors 102 ₁₋₃ remain in the same locations and orientations duringoperations of the machinery in the workspace 100. In one embodiment, theinitial registered state of the sensors can be stored in memory 210 sothat it can be retrieved later in case the system is not registeredduring operation and/or the workcell is moved to a new physicallocation. When one or more sensors 102 ₁₋₃ are accidentally moved ordrift out of their registered positions, the sensors may be misalignedrelative to each other and/or the machinery; as a result, the coveragearea of the sensors 102 ₁₋₃ may vary outside a predefined area and thecontrol outputs will be invalid and result in a safety hazard. Invarious embodiments, the same approaches used for initial registrationamong the sensors 102 ₁₋₃ and between the sensors 102 ₁₋₃ and themachinery described above can be extended to monitor (i) continuedaccuracy of registration among the sensors 102 ₁₋₃ and between thesensors 102 ₁₋₃ and the machinery during operation and (ii) the coverageareas of the sensors 102 ₁₋₃. For example, during initial registrationdescribed above, the control system 112 (e.g., the registration module239) may compute a set of metrics capturing the fit accuracy of theobserved data to a model of static elements in the workspace that iscreated during the registration process. These metrics may include, forexample, registration validation, real-time robot tracking, etc. As thesystem operates, the same metrics are recalculated in real time. If themetrics or deviations of the metrics from initial metric values (i.e.,obtained during initial registration) exceed a specified threshold,and/or if the coverage area is outside the bounds of what is expected isobserved, the registration during the system operation may be consideredto be invalid and an error condition may be triggered. Subsequently, therobot 106 and/or machinery may be transitioned to a safe state where therobot/machinery is operated with a reduced speed or deactivated.Additionally, if during operation of the machinery, the sensors 102 ₁₋₃remain in position but the fields of view are obscured or blocked,and/or the measured sensor signals are degraded (e.g., through somefailure of the system or through human action), the control system 112may determine that the outputs are invalid and then transition themachinery to the safe state.

FIG. 6 is a flow chart illustrating an exemplary approach for validatingregistrations among sensors and between the sensors and machinery duringoperation of machinery. In a first step 602, during initialregistrations among the sensors 102 ₁₋₃ and between the sensors 102 ₁₋₃and the machinery, the registration module 239 may compute a set ofmetrics (e.g., registration validation, real-time robot tracking, etc.)capturing the fit accuracy of the observed data to a model of staticelements in the workspace 100 that is created during the registrationprocess. Upon completion of the registrations and as the systemoperates, the registration module 239 may continuously update the samemetrics in real time (step 604). If the metrics or deviations of themetrics from initial metric values (i.e., obtained during initialregistration) exceed a specified threshold, and/or if the coverage areais outside the bounds of what is expected to be observed, theregistration during the system operation may be considered to be invalidand an error condition may be triggered (step 606). Subsequently, therobot 106 and/or machinery may be transitioned to a safe state where therobot/machinery is operated with a reduced speed or deactivated (step608). Additionally, the analysis module 237 may continuously analyze theacquired sensor signals during operation of the machinery (step 610). Ifthe sensors 102 ₁₋₃ remain in position but the fields of view areobscured or blocked, and/or the measured sensor signals are degraded(e.g., through some failure of the system or through human action), thecontrol system 112 may determine that the outputs are invalid and thentransition the machinery to the safe state (step 612). If the metrics ordeviations of the metrics from initial metric values do not exceed thespecified threshold, the coverage area is within the bounds of theexpected observation area, the fields of view of the sensors are notobscured or blocked, and the measured sensor signals are not degraded,the control system 112 may cause the machinery to continuously perform adesignated task (step 614).

The term “controller” or “control system” used herein broadly includesall necessary hardware components and/or software modules utilized toperform any functionality as described above; the controller may includemultiple hardware components and/or software modules and thefunctionality can be spread among different components and/or modules.For embodiments in which the functions are provided as one or moresoftware programs, the programs may be coded in a suitable language asset forth above. Additionally, the software can be implemented in anassembly language directed to the microprocessor resident on a targetcomputer; for example, the software may be implemented in Intel 80x86assembly language if it is configured to run on an IBM PC or PC clone.The software may be embodied on an article of manufacture including, butnot limited to, a floppy disk, a jump drive, a hard disk, an opticaldisk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gatearray, or CD-ROM. Embodiments using hardware circuitry may beimplemented using, for example, one or more FPGA, CPLD or ASICprocessors.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is: 1.-24. (canceled)
 25. A method of ensuring safeoperation of industrial machinery in a workcell, the method comprisingthe steps of: a. disposing a plurality of image sensors proximate to theworkcell; b. registering the sensors to each other in a common referenceframe; c. computationally relating the common reference frame of thesensors to a global frame of the workcell; d. registering the pluralityof sensors to the industrial machinery; and e. monitoring the industrialmachinery during operation thereof based at least in part on images ofthe workcell acquired by the sensors and the registration of the sensorsto each other and to the industrial machinery.
 26. The method of claim25, wherein the industrial machinery comprises at least a robot arm. 27.The method of claim 25, wherein the sensors are registered to each otheraccording to steps comprising acquiring, with at least some of thesensors, a first plurality of images of the workcell and registering thesensors to each other based at least in part on the first plurality ofimages.
 28. The method of claim 27, further comprising: f. generating aninitial accuracy metric indicating an accuracy level of the registrationof the plurality of sensors to the industrial machinery; and g.following step (f), during operation of the industrial machinery,determining whether a subsequent accuracy metric indicating an accuracylevel of the registration deviates from the initial accuracy metric bymore than a threshold amount, and if so, altering operation of theindustrial machinery.
 29. The method of claim 28, wherein step (g)comprises periodically analyzing a second plurality of images acquiredduring operation of the industrial machinery to (i) regenerate theaccuracy metric, (ii) compare the regenerated accuracy metric to theinitial accuracy metric to determine a deviation therebetween, and (iii)altering operation of the machinery if the deviation exceeds a thresholdvalue.
 30. The method of claim 29, wherein the metric comprises at leastone of registration validation or real-time robot tracking.
 31. Themethod of claim 25, further comprising implementing aglobal-optimization algorithm to register (i) the plurality of sensorsto each other and (ii) the plurality of sensors to the industrialmachinery.
 32. A control system for ensuring safe operation ofindustrial machinery in a workcell, the system comprising: a pluralityof image sensors proximate to the workcell; and a controller configuredto: register the sensors to each other in a common reference frame;computationally relate the common reference frame of the sensors to aglobal frame of the workcell; register the plurality of sensors to theindustrial machinery; and monitor the industrial machinery duringoperation thereof based at least in part on images of the workcellacquired by the sensors and the registration of the sensors to eachother and to the industrial machinery.
 33. The control system of claim32, wherein the controller is further configured to: cause at least someof the image sensors to acquire a first plurality of images of theworkcell; register the sensors to each other based at least in part onthe first plurality of images; and convert the first plurality of imagesto a common reference frame of the sensors.
 34. The control system ofclaim 33, wherein the controller is further configured tocomputationally analyze the first plurality of images to verify thatthere is sufficient overlap and sufficient distinction thereamong. 35.The control system of claim 32, wherein the controller is furtherconfigured to: cause at least one of the sensors to acquire an image ofa scene in the workcell; and determine one or more pairs of discretefeatures on the image of the scene, wherein the plurality of sensors isregistered to the industrial machinery based at least in part on the oneor more pairs of discrete features.
 36. The control system of claim 32,wherein the image of the scene comprises 3D point cloud data mapping theworkcell.
 37. The control system of claim 36, wherein the image of thescene comprises a 2D or 3D CAD model of at least one of the industrialmachinery or the workcell.
 38. The control system of claim 36, whereinthe controller is further configured to cause the sensors to perform a2D or 3D scan on the industrial machinery or the workcell, the image ofthe scene comprising a model of the industrial machinery or the workcellconstructed based at least in part on the 2D or 3D scan.
 39. The controlsystem of claim 32, wherein the controller is further configured to:generate an initial accuracy metric indicating an accuracy level of theregistration of the plurality of sensors to the industrial machinery;and during operation of the industrial machinery, determine whether asubsequent accuracy metric indicating an accuracy level of theregistration deviates from the initial accuracy metric by more than athreshold amount, and if so, alter operation of the industrialmachinery.
 40. The control system of claim 39, wherein the controller isfurther configured to: cause the sensors to periodically acquire asecond plurality of images during operation of the industrial machinery;regenerate the accuracy metric; compare the regenerated accuracy metricto the initial accuracy metric to determine a deviation therebetween;and alter operation of the machinery if the deviation exceeds athreshold value.
 41. The control system of claim 40, wherein the metriccomprises at least one of registration validation or real-time robottracking.
 42. The control system of claim 32, wherein the controller isconfigured to execute a global-optimization algorithm to register (i)the plurality of sensors to each other and (ii) the plurality of sensorsto the industrial machinery.